docs: def _rottrip(ang: np.ndarray) -> np.ndarray:
      """
      transformation matrix
  
      Parameters
      ----------
  
      ang : N x 3 numpy.ndarray
          angle to transform (radians)
      """
      ang = ang.squeeze()
      if ang.size > 1:
          raise ValueError('only one angle allowed at a time')
  
      return np.array([[np.cos(ang), np.sin(ang), 0],
                       [-np.sin(ang), np.cos(ang), 0],
                       [0, 0, 1]])